This invention relates to a navigation system for a motor vehicle by which a route to be taken is displayed by a cathode ray tube CRT screen, a liquid crystal display, or another display means to navigate the vehicle. More particularly, this invention relates to such a navigation system provided with a route determination process by which a desired route can be determined readily and correctly.
A known navigation system is provided with a screen on which a road map is displayed. In one type of such a system, a route is determined by pinpointing and thereby inputting, with a cursor on the screen or by means of a light pen, desired intersections on the displayed road map consecutively from a starting point to a destination. In another type of system, once a starting point and destination are input, a shortest route from the starting point to the destination is automatically determined, according to map data previously stored, and indicated on the road map displayed by the screen.
These types of navigation systems, however, have the following shortcomings.
During route determination using the former type of navigation system, if there lies ahead, in the direction designated by the cursor or light pen, an intersection of roads that form a small angle with regard to each other or an intersection of a plurality of roads, an undesired route may be determined. In this case, the user has to return the cursor or other designating means to the previous location, and again instruct the system to determine a route.
On the other hand, the latter type of system also falls short, in spite of its operation facility, because it uses previously stored and not up-dated program data in determining a route. When unexpected repair work is underway at the automatically selected route, or when the route the user preferred is not selected, the user has to correct the route, after completion of the automatic route determination, in the same laborious manner as in the former type of navigation system.